Pressure sensors are generally used in avionics applications to measure the flight-related “air data” parameters of altitude, altitude rate, airspeed, airspeed rate, Mach, Mach rate, and other related parameters based in part on various air pressures measured in flight. These parameters are typically derived from two primary pressure measurements—static pressure, that is indicative of the ambient pressure at the aircraft's flight altitude, and total pressure, that is the summation of the static pressure and a higher pressure induced by the aircraft's forward velocity.
Recent mandates in international flight regulations require aircraft to fly with reduced vertical separation between adjacent flight levels. This vertical separation has been reduced from 2,000 foot spacing down to 1,000 foot spacing for aircraft flying between 29,000 and 41,000 feet above mean sea level. This decrease in spacing enables double the number of aircraft to occupy any given flight corridor at a given time, thereby reducing in-flight traffic delays. It, however, requires aircraft to be controlled more precisely at their assigned altitude to minimize the risk of collision.
Since on-aircraft measurement of the altitude is dependent on precisely measuring static pressure, and to a lesser extent total pressure due to some of the speed-based corrections that are typically applied to correct for airflow anomalies over the static ports, extremely precise, stable, quiet, low latency, high resolution pressure measurements must be accomplished in order to yield the required accuracy. The quietness, latency and resolution of these measurements are essential considerations necessary to provide timely dynamic correction signals to the autopilot for maintaining the assigned altitude, Mach number, and airspeed.
Most air data sensors interface with their processing electronics in a manner where their information is sampled and/or computed at discrete times based on the air data computer's interrupt-based timing loops. Sampling at discrete points in such systems is prone to aliasing of signals above the Nyquist frequency and noise; therefore, prefiltering is necessary to minimize those detrimental effects. Prefiltering, however, adds latency and decreases system responsiveness. Since rate-based calculations such as altitude rate, Mach rate, and airspeed rate are mathematical derivative functions versus time, any jitter in the time of data measurement and its processing by the system's computer becomes the main contributor affecting the quietness and usable resolution of such rate parameter measurements. Traditionally, this noise has been reduced by heavy filtering, again, at the penalty of increased latency.
Although there are many different Integrated Sensor Systems (ISS) in the marketplace, none currently simultaneously provide adequate interface flexibility, measurement capability, long-term stability, and measurement resolution for wide bandwidth, low noise air data and other precision applications. Moreover, many so-called “smart sensors” (those with an internal microcomputer) have inadequate capability to simultaneously perform high accuracy, high resolution pressure measurements at the high measurement rates that may be needed for modern air data and other applications requiring low latency and wide bandwidth.
Hence, there is a need for a precision, environmentally-compatible, integrated sensor system that incorporates a sensor and unique analog to digital conversion and interface circuitry within a single housing and is capable of providing data from which low latency, low noise static pressure and pressure-based rate functions may be externally computed. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.